The Institute's shift to environmental skepticism began with the publication of a report on global warming by William Nierenberg. During the United States presidential election, 1988, George H. W. Bush had pledged to meet the "greenhouse effect with the White House effect."[2] Nierenberg's report, which blamed global warming on solar activity, had a large impact on the incoming Bush presidency, strengthening those in it opposed to environmental regulation.[2] In 1990 the Institute's founders (Jastrow, Nierenberg and Seitz) published a book on climate change.[4] The appointment of David Allan Bromley as presidential science advisor, however, saw Bush sign the United Nations Framework Convention on Climate Change in 1992, despite some opposition from within his administration.[2]

In 1994, the Institute published a paper by its then chairman, Frederick Seitz, titled Global warming and ozone hole controversies: A challenge to scientific judgment. Seitz questioned the view that CFCs "are the greatest threat to the ozone layer".[5] In the same paper, commenting on the dangers of secondary inhalation of tobacco smoke, he concluded "there is no good scientific evidence that passive inhalation is truly dangerous under normal circumstances."[6]

Politicizing Science: The Alchemy of Policymaking is a book by the George C. Marshall Institute, edited by Michael Gough (author). Gough advocates a sort of disinterested objectivity on the part of scientists and policymakers: Ideally, the scientists or analysts who generate estimates of harm that may result from a risk would consider all the relevant facts and alternative interpretations of the data, and remain skeptical about tentative conclusions. Ideally, too, the agency officials and politicians, who have to enact a regulatory program, would consider its costs and benefits, ensure that it will do more good than harm, and remain open to options to stop or change the regulation in situations where the underlying science is tentative. [1]

Since 1989 GMI has been involved in what it terms "a critical examination of the scientific basis for global climate change policy." [9] The Institute was described as a "central cog in the denial machine" in a Newsweek cover story on global warming.[10]

In Requiem for a Species (2010), Clive Hamilton is critical of the Marshall Institute and contends that the conservative backlash against global warming research was led by three prominent physicists -- Frederick Seitz, Robert Jastrow, and William Nierenberg, who founded the Institute in 1984. According to Hamilton, by the 1990s the Marshall Institute's main activity was attacking climate science.[11]Naomi Oreskes and Erik M. Conway reach a similar conclusion in Merchants of Doubt (2010), where they identified a few contrarian scientists associated with conservative think-tanks who fought the scientific consensus and spread confusion and doubt about global warming.[12]

William O'Keefe, chief executive officer of the Marshall Institute, questions the methods used by advocates of new government restrictions to combat global warming: "We have never said that global warming isn't real. No self-respecting think tank would accept money to support preconceived notions. We make sure what we are saying is both scientifically and analytically defensible."[17]

Matthew B. Crawford, author of Shop Class as Soulcraft: An Inquiry Into the Value of Work,[18] was appointed executive director of GMI in September 2001.[19] He left the GMI after 5 months, saying that the institute was "fonder of some facts than others". He contended a conflict of interest existed in the funding of the institute.[20] In Shop Class as Soulcraft, he stated about the Institute:

“

...the trappings of scholarship were used to put a scientific cover on positions arrived at otherwise. These positions served various interests, ideological or material. For example, part of my job consisted of making arguments about global warming that just happened to coincide with the positions taken by the oil companies that funded the think tank.

Exxon-Mobil was a funder of the GMI until it pulled funding from it and several similar organizations in 2008.[23] From 1998-2008, the institute received a total of $715,000 in funding from Exxon-Mobil.[24]